Method and device for transmitting and receiving data in mobile communication system

ABSTRACT

The present specification relates to a communication method and a communication device, and a random access method of a user equipment (UE), according to one embodiment of the present specification, comprises the steps of: sensing a random access trigger in a connected state; determining the type of the random access trigger when the random access trigger is sensed; and performing congestion control if the type of the random access trigger is a preset type.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 15/601,833filed May 22, 2017, which is a continuation of application Ser. No.14/403,147, now U.S. Pat. No. 9,661,526, which is the National Stage ofInternational Application No. PCT/KR2013/004459, filed May 21, 2013,which claims the benefit of Provisional Application No. 61/649,910 filedMay 21, 2012, and Provisional Application No. 61/658,617, filed Jun. 12,2012, the disclosures of which are herein incorporated by reference.

BACKGROUND 1. Field

The present invention relates to a method and apparatus for transmittingand receiving data in the mobile communication system.

2. Description of Related Art

Mobile communication systems were developed to provide mobile users withcommunication services. With the rapid advance of technologies, themobile communication systems have evolved to the level capable ofproviding high speed data communication service beyond the earlyvoice-oriented services.

Recently, standardization for a Long Term Evolution (LTE) system, as oneof the next-generation mobile communication systems, is underway in the3^(rd) Generation Partnership Project (3GPP). LTE is a technology forrealizing high-speed packet-based communications with the data rate ofup to 100 Mbps, which is higher than the currently available data rate,and its standardization is almost complete.

In line with the completion of the LTE standardization, an LTE-Advanced(LTE-A) system is now under discussion, which improves a transfer rateby combining the LTE communication system with several new technologies.One of such technologies is Carrier Aggregation. The Carrier Aggregationis a technology allowing a terminal to use multiple downlink carriersand multiple uplink carriers unlike the conventional technology of usingone downlink carrier and one uplink carrier for data communication.

Assuming that a cell is configured with one downlink carrier and oneuplink carrier in the conventional concept, the carrier aggregation canbe understood as if the UE communicates data via multiple cells. Withthe use of carrier aggregation, the peak data rate increases inproportion to the number of aggregated carriers.

In the following description, if a UE receives data through a certaindownlink carrier or transmits data through a certain uplink carrier,this means to receive or transmit data through control and data channelsprovided in cells corresponding to center frequencies and frequencybands characterizing the carriers.

In the present Invention, carrier aggregation may be expressed asconfiguring a plurality of serving cells. At this time, the pluralityserving cells include a primary serving cell (PCell) and secondaryserving cell (SCell).

Other terms to describe the embodiments of the present invention areused in the meanings as used in the LTE system and specified in TS36.331and TS36.321 (December, 2011).

In line with the widespread use of smartphone an always-on typeservices, the number of terminals in connected state increases and, as aconsequence, this increases the probability of congestion on the randomaccess channel. An embodiment of the present invention proposes a methodand apparatus for applying congestion control to the terminal in theconnected state to solve the above problem.

As aforementioned, the introduction of the carrier aggregation increasesthe achievable data rate dramatically, it is restrictive to increase thedata rate actually doe to the intrinsic problem of layer 2 (e.g. shortlength of sequence number). An embodiment of the present inventionproposes a method and apparatus to extend the layer sequence number.

SUMMARY

The present invention aims to provide a method and apparatus ofpreventing occurrence of cell congestion.

In accordance with an aspect of the present invention, a random accessmethod of a User Equipment (UE) includes detecting a random accesstrigger in a connected state, checking a type of the random accesstrigger, performing, when the random access trigger is a predeterminedtype, congestion control.

In accordance with another aspect of the present invention, a UserEquipment (UE) which performs random access includes a controller whichdetects a random access trigger in a connected state, checks a type ofthe random access trigger, and performs, when the random access triggeris a predetermined type, congestion control.

In accordance with another aspect of the present invention, acommunication method of a base station includes broadcasting congestioncontrol information for use in a random access procedure of a UserEquipment (UE) in a connected state. The congestion control informationincludes a threshold value to be compared with a value generatedrandomly for determining whether the UE in the connected state performsthe random access procedure for uplink transmission.

In accordance with still another aspect of the present invention, a basestation includes a communication unit which broadcasts congestioncontrol information for use in a random access procedure of a UserEquipment (UE). The congestion control information includes a thresholdvalue to be compared with a value generated randomly for determiningwhether the UE in the connected state performs the random accessprocedure for uplink transmission.

The method and apparatus of the present invention is advantageous interms of preventing occurrence of cell congestion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating LTE system architecture to whichvarious embodiments of the present disclosure are applied;

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

FIG. 3 is a diagram illustrating intra-eNB carrier aggregation.

FIG. 4 is a signal flow diagram illustrating the random accessprocedure.

FIG. 5 is a flowchart illustrating a congestion control procedure of theUE according to the first embodiment of the present invention.

FIG. 6 is a signal flow diagram illustrating the communication procedureaccording to the second embodiment of the present invention.

FIG. 7A is a diagram illustrating a PDCP PDU format having a 7-bitsequence number.

FIG. 7B is a diagram illustrating a PDCP PDU formation having a 12-bitsequence number.

FIG. 7C is a diagram illustrating a PDCP PDU format having a 15-bitsequence number (extended sequence number).

FIG. 8 is a signal flow diagram illustrating the handover procedureaccording to the third embodiment of the present invention.

FIG. 9 is a diagram illustrating the local transfer according to thethird embodiment of the present invention.

FIG. 10 is a flowchart illustrating the handover procedure of the UE 805according to the third embodiment of the present invention.

FIG. 11 is a diagram illustrating a format of the PDCP STATUS REPORTaccording to the third embodiment of the present invention.

FIG. 12 is a signal flow diagram illustrating a communication procedureaccording to the fourth embodiment of the present invention.

FIG. 13 is a flowchart illustrating the SCell configuration messageprocessing procedure according to the fourth embodiment of the presentinvention.

FIG. 14 is a flowchart illustrating the A/C MAC CE message processingprocedure of the UE 1205 according to an embodiment of the presentinvention.

FIG. 15 is a diagram illustrating a format of the payload.

FIG. 16 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

FIG. 17 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

A detailed description is made of the representative embodiments toachieve the above technical objects. The same reference numbers are usedthroughout the drawings to refer to the same or like parts. However, thepresent invention is not limited by the terms used for explanationconvenience but can be even to other systems having the similartechnical background with a slight modification, without departing fromthe spirit and scope of the present invention.

Exemplary embodiments of the present invention are described in detailhereinafter with reference to the accompanying drawings.

FIG. 1 is a diagram illustrating LTE system architecture to whichvarious embodiments of the present disclosure are applied.

Referring to FIG. 1, the radio access network of the mobilecommunication system includes evolved Node Bs (eNBs) 105, 110, 115, and120, a Mobility Management Entity (MME) 125, and a Serving-Gateway(S-GW) 130. The User Equipment (hereinafter, referred to as UE) 135connects to an external network via eNBs 105, 110, 115, and 120 and theS-GW 130.

The eNBs 105, 110, 115, and 120 are connected to the UE 135 throughradio channels. The eNBs 105, 110, 115, and 120 allow correspond to thelegacy node Bs of the UMTS system but are responsible for complicatedfunctions as compared to the legacy node B

In an exemplary LTE system, all the user traffic including real timeservices such as Voice over Internet Protocol (VoIP) are providedthrough a shared channel.

Accordingly, there is a need of a device for scheduling data based onthe state information such as buffer states, power headroom states, andchannel states of the UEs; and the eNBs 105, 110, 115, and 120 areresponsible for the function. Particularly, the LTE system adoptsOrthogonal Frequency Division Multiplexing (OFDM) as a radio accesstechnology to secure the data rate of up to 100 Mbps.

The UE 135 uses Adaptive Modulation & Coding (AMC). AMC is a technologyof determining the modulation scheme and channel coding rate inadaptation to the channel condition.

The S-GW 130 is an entity to provide data bearers so as to establish andrelease data bearers under the control of the MME 125. The MME 125 isresponsible for mobility management of UEs and various control functionsand may be connected to a plurality of eNBs.

FIG. 2 is a diagram illustrating a protocol stack of the LTE system towhich the present invention is applied.

Referring to FIG. 2, the protocol stack of the LTE system includesPacket Data Convergence Protocol (PDCP) 205 and 240, Radio Link Control(RLC) 210 and 235, Medium Access Control (MAC) 215 and 230, and Physical(PHY) 220 and 225.

The PDCP layer 205 and 240 is responsible for IP headercompression/decompression. The RLC layer 210 and 235 is responsible forsegmenting the PDCP Protocol Data Unit (PDU) into segments inappropriate size for Automatic Repeat Request (ARQ) operation.

The MAC layer 215 and 230 is responsible for establishing connection toa plurality of RLC entities. The MAC layer 215 and 230 multiplexes theRLC PDUs into MAC PDUs and delivers the MAC PDUs to the PHY layer 220and 25. The MAC layer 215 and 230 also demultiplexes the MAC PDUs fromthe PHY layers 220 and 225 into RLC PDUs and delivers the RLC PDUs tothe RLC entities.

The PHY layer 220 and 225 performs channel coding and modulation on theupper layer data to generate OFDM symbols and transmit the OFDM symbolsover radio channel. The PHY layer 220 and 225 performs demodulation andchannel decoding on the OFDM symbols received over the radio channel anddeliver the decoded data to the upper layer.

FIG. 3 is a diagram illustrating intra-eNB carrier aggregation.

Referring to FIG. 3, an eNB transmits and receives signals to and fromthe UE 330 through multiple carriers across a plurality of frequencybands.

For example, it is typical for the eNB 305 using multiple carriershaving downlink center frequency f1 513 and f2 310 to transmit andreceive to and from the UE 330 through one of the multiple carriers.However, the CA-enabled UE 330 is capable of transmitting signals on themultiple carriers.

In this way, the eNB 305 is capable of allocating carriers or servingcells to the carrier aggregation-enabled UE 330 in adaptation to thechannel condition to increase the data rate of the UE 330.

Unlike the exemplary situation of FIG. 3, the signals can be transmittedreceived by means of a transmission/reception device installed atlocations far from the eNB geographically such as Remote Radio Head(RRH). At this time, it is preferred for the UE to set uplinktransmission timings in the serving cells of the transmission/receptiondevices located at the same place as the eNB and thetransmission/reception devices located at other places such as RRH todifferent values. This is because the propagation delay environments ofthe two serving cells are likely to be different considerably.

If the UE is configured with SCell of which location differs from thatof the PCell so as to have an uplink transmission timing different fromthat of the PCell, it is necessary for the UE to perform a random accessprocedure in the SCell to determine the uplink transmission timing.

FIG. 4 is a signal flow diagram illustrating the random accessprocedure.

The random access procedure is made up of 4 steps, i.e. transmittingpreamble, receiving random access response, transmitting message 3, andreceiving contention resolution.

If a random access is triggered by a certain reason, the UE 405determines the preamble transmission timing, transmission resource(frequency and time resources), and type of the preamble based on therandom access transmission resource information of the cell in which therandom access is performed. The UE transmits the preamble at thepreamble transmission power calculated based on the current channelcondition, e.g. pathloss, at step 415.

Upon receipt of the preamble transmitted by the UE, the eNB 410 sendsthe UE 405 a response message in reply thereto at step 420. The responsemessage may include uplink Timing Advance (TA) of the UE or uplinktransmission resource information (UL grant) for message 3 transmission.

If the response message is received, the UE 405 transmits the message 3at step 425. The message 3 includes UE identifier and, if the message 3is received successfully, the eNB transmits a response called ContentionResolution at step 430. If no preamble is received, the eNB 410 does nottransmit the response message and thus the UE 405 fails receiving theresponse message. The UE 405 retransmits the preamble at a transmitpower increased by predetermined amount, as a part of uplink powercontrol, after a lapse of a predetermined time period.

If cell congestion occurs, the eNB performs congestion control. Oneexample of the congestion control is Access Class Barring (ACB) (seeTS36.331). The ACB is a technique of controlling the random access ofthe UEs in the idle state. According to the ACB, the UE in the idlestate determines whether to perform random access statistically based onthe ACB parameters broadcast in the system information. This makes itpossible to avoid the problem occurring when all of the UEs in the idlestate perform random access simultaneously in the cell congestionenvironment.

The UE in the connected state may be allocated Dedicated SchedulingRequest (D-SR) transmission resource, and the UE in the connected statewhich is configured with the D-SR transmission resource performs randomaccess in a very restricted case. By taking notice of current tendencyof increase of the number of UEs in the connected state due to thewidespread use of smartphone and increase of always-on type services, itmay be impossible to allocate D-SR transmission resource to all the UEsin the connected state. The increase of the number of UEs which are notallocated D-SR transmission resource may increases the random accessload. There is therefore a need of controlling the random access byapplying the congestion control scheme such as ACB even to the UEs inthe connected state.

The UE in the connected state may perform random access in four cases asfollows.

1. The eNB instructs the UE in the connected state to perform randomaccess.

2. High priority UL data occurs in the state where no uplinktransmission resource is allocated to the UE in the connected state.

3. The UE in the connected state has found a cell of which channelquality is higher than a predetermine threshold in the ConnectionReestablishment procedure.

4. The UE in the connected state is performing handover.

In the first case, the random access is triggered by direction controlof the eNB and thus there is no need of applying ACB or similar scheme.Since the RRC Connection Reestablishment procedure affects significantlyto the user's sensible service quality, it is not preferred to delay therandom access by applying the ACB or similar scheme. If the randomaccess is delayed due to the ACB or similar scheme, this is likely tocause handover failure. Accordingly, in some embodiments of the presentinvention, the congestion control for random access of the UE in theconnected state is applied only to the resume of uplink transmission.

The eNB transmits the information about the congestion control using thesystem information of the cell in which the congestion occurs among thecells under its control. This information may be ACB-related informationor similar type information or another type of information for the UE inthe connected state. As aforementioned, the ACB aims to control the RRCconnection establishment attempt of the UE in the idle state distinctlydepending on the purpose of the RRC connection establishment attempt.The ACB information is broadcast in the System Information Block type 2(SIB 2) and made up of three informations as follows.

i) ac-BarringForEmergency, ii) ac-BarringForMO-Signalling, iii)ac-BarringForMO-Data

The ac-BarringForEmergency is the information controlling the connectionsetup for emergency call. The ac-BarringForMO-Signalling is theinformation controlling the connection setup for transmitting signalinginformation such as Tracking Area Update (TAU). The ac-BarringForMO-Datais the information controlling the connection setup for user datatransmission of the UE. Among the three informations, theac-BarringForMO-Data may be used for controlling the use of randomaccess in the connected state. This is because the random access of theUE in the connected state is performed to transmit user data in mostcases.

Some embodiments of the present invention provide a method of using theac-BarringForMO-Data of ACB or the like or separate information forcongestion control of the UE in the connected state.

In the case of using a different type of information instead of theac-BarringForMO-Data for congestion control, the separate informationmay include BarringPriority and BarringTime. The separate informationmay be broadcast in a predetermined system information block, e.g. SIBtype 15.

The UE in the RRC connected state monitors the connected state controlinformation continuously and, when random access is required for acertain reason, determines whether to start random access based on thecongestion control information.

FIG. 5 is a flowchart illustrating a congestion control procedure of theUE according to the first embodiment of the present invention.

The UE transitions to the idle state for a certain reason at step 505.The UE initiates random access procedure by sending an RRC ConnectionRequest control message, and the eNB sends the UE a RRC Connection Setupcontrol message. After the RRC connection setup, the UE performs regularoperation in the cell. The UE determines whether the serving cellsupports connected state congestion control. If the serving cellsupports the connected state congestion control, the UE acquires systeminformation, particularly, the connected state congestion controlinformation, and keeps the information up to date. The eNB notifies theUE whether the serving cell is of supporting the connected statecongestion control using a predetermined indicator included in the RRCConnection Configuration control message or, if in the course ofperforming handover, the RRC Connection Reconfiguration control message.

If the current serving cell does not support the connected statecongestion control, the UE in the connected state initiates randomaccess without any determination process when the random access istriggered. In the embodiment of FIG. 5, it is assumed that the servingcell supports the connected state congestion control.

If the current serving cell supports the connected state congestioncontrol, the UE keeps the connected state congestion control informationup to date at step 510. The UE stores the connected state congestioncontrol information acquired through the SIB type 2 or SIB type 15 andthen monitors the system information to detect any change therein. Ifthe system information changes, the UE acquires the changed information.

If the random access is triggered by a certain reason at step 515, theUE determines checks the type of the random access trigger at step 520.If the random access trigger type is a first type, the procedure goes tostep 530 in order to apply the congestion control. If the random accesstrigger type is a second type, the procedure goes to step 525.

In the embodiment of FIG. 5, the first type random access includes ‘therandom access which is triggered to resume uplink transmission.’ Forexample, if the following conditions are all fulfilled, the UEdetermines that the random access is triggered for resuming uplinktransmission.

<Conditions for Determining Random Access Triggered for Resuming ULTransmission>

1. A regular Buffer Status Report (BSR) is triggered is triggered at acertain UE at a certain timing.

2. No Scheduling Request (SR) transmission resource of Physical UplinkControl Channel (PUCCH) is allocated to the UE.

3. The priority of the logical channel on which the regular BSR istriggered is lower than a predetermined threshold.

4. The data triggered the regular BSR is neither Common Control ChannelService Data Unit (CCCH SDU) such as RRC connection reestablishmentrequest message nor RRC connection reconfiguration complete message.

The BSR is the control information for reporting UE buffer state to theeNB. The BSR may be performed with one of a short BSR format and a longBSR format. The BSR may carry the Buffer Status (BS) of at least one andup to 4 Logical Channel Group (LCG). The short BSR is used when there isone LCG having the data to be transmitted and is composed of the LCGidentifier and BS. The long BSR is used to report the buffer status offour LCGs and contains the BSs of the LCGs in an order of the LCGidentifiers. The LCG is a set of the logical channel grouped under thecontrol of the eNB, and the logical channels have similar logicalchannel priorities. The buffer status of the LCG is the sum of thebuffer status related to the logical channels included in the LCG andshows the data amount that can be transmitted among the data of RLCtransmission buffer, retransmission buffer, PDCP transmission buffer ofthe logical channels. The BSR may be triggered periodically or when apredetermined condition is fulfilled, e.g. when the data having apriority higher than that of the currently stored data occurs. Theformer is referred to as periodic BSR, and the latter is referred to asregular BSR. If the regular is triggered, the UE acquires thetransmission resource or the regular BSR through the random accessprocedure or the SR transmission resource. The SR transmission resourcemay be the transmission resource occurring periodically on the PhysicalUplink Control Channel (PUCCH and may be configured to the UE throughRRC connection setup procedure. The eNB may not be able to allocate SRtransmission resource to all UEs. The UE which is not allocated the SRtransmission resource initiate random access procedure.

The second type random access may include several cases as follows.

1. Random access triggered for handover. Or random access fortransmitting handover complete control message in the target cell.

2. Random access triggered by the eNB transmitting predetermined controlinformation (Physical Downlink Control Channel (PDCCH) order) to the UE.

3. Random access triggered by the UE transmitting RRC ConnectionReestablishment Request control message in the RRC connectionreestablishment procedure.

4. Random access triggered by the UE using a dedicated preamble.

The dedicated preamble is a preamble designated by the eNB, and the eNBmay allocate the dedicated preamble to the UE in the course ofinstructing the UE to perform random access or handover.

If the second type random access is triggered, the procedure goes tostep 525 at which the UE performs the random access without anydetermination process although the connected state congestion controlinformation is broadcast in the current serving cell or the serving cellsupports the connected state congestion control. The random accessprocedure is performed in such a way that the UE transmits a randomaccess preamble in a certain serving cell, monitors PDCCH of the servingcell to receive a random access response message, and performs uplinktransmission based on the uplink grant contained in the random accessresponse message in the serving cell through which the random accesspreamble has been transmitted.

If the first type random access is triggered, the procedure goes to step530 at which the UE determines whether to apply the connected statecongestion control. For example, if the following connected congestioncontrol application conditions are all fulfilled, the UE determines thatit is necessary to apply the congestion control and thus the proceduregoes to step 535. If any of the following conditions is not fulfilled,the UE determines that it is not necessary to apply the congestioncontrol and thus the procedure goes to step 525.

<Conditions for Applying Connected State Congestion Control>

1. The connected state congestion control information is broadcast inthe current serving cell.

2. It fails to pass the test for applying the congestion control.

The connected state congestion control information may be provided inthe form of ac-BarringForMO-Data or ac-BarringForMO-Data-Connected. Theac-BarringForMO-Data is broadcast in the SIB type 2, and theac-BarringForMO-Data-Connected in the SIB type 15. Theac-BarringForMO-Data includes ac-BarringFactor and ac-BarringTime, andthe ac-BarringForMO-Data-Connected includes BarringFactor,BarringPriority, and BarringTime.

In the case of the connected state congestion control information in theform of ac-BarringForMO-Data, the UE generates a random real number inthe range from 0 to 1 and, if the real number is greater than theac-BarringFactor, determines that the congestion control applicationtest succeeds and, otherwise real number is less than theac-BarringFactor, the UE determines that the congestion controlapplication test fails.

In the case of the connected state congestion control information in theform of ac-BarringForMO-Data-Connected, the UE compares the priority ofthe data triggered the regular BSR with the BarringPriority. If thepriority of the data is higher than the BarringPriority, the UEdetermines that the congestion control application test succeeds.Otherwise if the priority of the data is lower than the BarringPriority,the UE generates a random real number in the range from 0 to 1 anddetermines, if the real number is greater than the BarringFactor, thatit has passed the test and, otherwise if the real number is less thanthe BarringFactor, it has failed the test.

At step 535, the UE cancels the regular BSR to prevent random accessattempt. The UE configures a timer Tbarring and, if the data triggeredthe regular BSR is in the buffer yet and if there is no other data withhigher priority, the UE retriggers the regular BSR at step 540. If theconnected congestion control information is the ac-BarringForMO-Data,the Tbarring is set by equation (1).Tbarring=(0.7+0.6*rand)×ac-BarringTime  (1)

If the connected congestion control information is theac-BarringForMO-Data-Connected, the Tbarring is set by equation (2).Tbarring=(0.7+0.6*rand)×BarringTime  (2)

In equations (1) and (2), rand denotes a real number selected randomlyin the range from 0 to 1.

A description is made of another congestion control method of the UE inthe connected state hereinafter.

It may fail to allocate D-SR transmission resource to all the UEs in theconnected state. It is the case especially in consideration of thecurrent tendency of increase of the number of UEs in the connected statedue to the popularity of smartphones and always-on type services. Theincrease of the number of UEs which are not allocated the D-SRtransmission resource is likely to increase the random access load. Inorder to mitigate the random access load, the present invention proposesa method of applying the random access resource selectively depending onthe logical channel for transmitting the data in the situation where theUEs in the connected state attempt random access.

FIG. 6 is a signal flow diagram illustrating the communication procedureaccording to the second embodiment of the present invention.

In FIG. 6, the mobile communication includes a UE 605 and an eNB 610.The UE 605 powers on at step 620. The UE 605 searches for a cell ofwhich electric wave is received and a Public Land Mobile Network (PLMN)through a search procedure and determines the PLMN and cell to establisha connection based thereon at step 625.

The UE 650 performs the RRC Connection Setup procedure through theselected cell at step 630. The UE transmits a preamble, receives arandom access response message transmitted by the eNB 610 in reply, andtransmits to the eNB 610 a control message requesting for RRC Connectionbased on the uplink grant included in the random access responsemessage. Upon receipt of the message, the eNB 610 sends the UE 605 anRRC Connection Setup message, and the UE 605 configures the SignalingRadio Bearer (SRB) for RRC control message transmission such that theRRC connection establishment procedure completes. After the RRCconnection setup procedure, the UE 605 and an MME performs aregistration procedure, and the eNB 610 acquires UE information in theregistration procedure and stores and manages the context of the UE 650,as shown in FIG. 12.

If it is determined to configure Data Radio Bearer (DRB) to the UE 605for data communication, the eNB sends the UE 605 an RRC ConnectionReconfiguration message including the radio bearer configurationinformation. If the UE 605 is not allocated D-SR resource and if thereis large number of UEs which are not allocated the D-SR resource, theeNB 610 determines to allocate Physical Random Access Channel (PRACH)mask index per Logical Channel (LCH) or LCH Group (LCG) at step 635. TheLCH is the logical channel mapped to the radio bearer one by one andworks as a path between RLC entity of the radio bearer and a MAC entity.

The PRACH mask index is an integer in the range from 0 to 15 and definedfor use in Frequency Division Duplex (FDD) and Time Division Duplex(TDD) modes as shown in table 1.

TABLE 1 PRACH Mask Available PRACH Available PRACH Index resource (FDD)resource (TDD) 0 All All 1 PRACH Resource Index 0 PRACH Resource Index 02 PRACH Resource Index 1 PRACH Resource Index 1 3 PRACH Resource Index 2PRACH Resource Index 2 4 PRACH Resource Index 3 PRACH Resource Index 3 5PRACH Resource Index 4 PRACH Resource Index 4 6 PRACH Resource Index 5PRACH Resource Index 5 7 PRACH Resource Index 6 Reserved 8 PRACHResource Index 7 Reserved 8 PRACH Resource Index 8 Reserved 10 PRACHResource Index 8 Reserved 11 Every, in the time domain, Every, in thetime domain, even PRACH opportunity even PRACH opportunity 1^(st) PRACHResource 1^(st) PRACH Resource Index in subframe Index in subframe 12Every, in the time domain, Every, in the time domain, odd PRACHopportunity odd PRACH opportunity 1^(st) PRACH Resource 1^(st) PRACHResource Index in subframe Index in subframe 13 Reserved 1^(st) PRACHResource Index in subframe 14 Reserved 2^(nd) PRACH Resource Index insubframe 15 Reserved 3^(rd) PRACH Resource Index in subframe

If the PRACH mask index n is configured to the LCH x or LCG x′, this hasthe following meaning.

If the available PRACH resource indicated by the PRACH mask index n ism, the random access for the regular BSR related to the LCH x or LCG x′may be initiated in the intersection between the PRACH resourcedetermined by the PRACH resource index m and the PRACH resourceconfigured in the current cell.

The PRACH resource index (or PRACH configuration index) indicates thetime/frequency resource region available for transmitting random accesspreamble. The PRACH configuration index is defined distinctively for FDDand TDD due to the difference in frame structure between the TDD andFDD, as shown in table 2 for FDD and table 5.7.1-3 of TS 36.211 for TDD.

TABLE 2 PRACH Configuration Preamble System frame Index Format numberSubframe number 0 0 Even 1 1 0 Even 4 2 0 Even 7 3 0 Any 1 4 0 Any 4 5 0Any 7 6 0 Any 1, 6 7 0 Any 2, 7 8 0 Any 3, 8 8 0 Any 1, 4, 7 10 0 Any 2,5, 8 11 0 Any 3, 6, 8 12 0 Any 0, 2, 4, 6, 8 13 0 Any 1, 3, 5, 7, 8 14 0Any 0, 1, 2, 3, 4, 5, 6, 7, 8, 8 15 0 Even 8

The eNB 610 determines the PRACH mask index to be allocated inconfiguring the logical channel or logical channel group to the UE 605.The logical channel/logical channel group with high priority or weightmay be allocated a PRACH mask index including more PRACH resource, andthe logical channel/logical channel group with low priority or weightmay be allocated the PRACH mask index including less PRACH resource.Certain logical channels, e.g. logical channels/logical channel groupsmapped to SRB, might have been allocated a predetermined PRACH maskindex implicitly such that only the rest logical channels/logicalchannel groups are allocated the PRACH mask indices. The PRACH maskindex allocated implicitly may be the PRACH index 0.

Some of the reserved values of the PRACH mask index (13˜15 in FDD, and7˜10 in TDD) may be used for special purpose. For example, one of thereserved values (hereinafter, referred to as R for explanationconvenience) may be used for indicating the resource other than thePRACH resource allocated to the logical channels/logical channel groupswith the exception of the logical channel/logical channel group mappedto SRB among the PRACH resources configured to the current serving cell.For example, the UE 605 is allocated LCG 0, LCG 1, and LCG 4; the LCG 1is allocated the PRACH mask index 1; the duplex mode of thecorresponding serving cell is FDD; and the PRACH configuration index is13. This means that the PRACH mask index of LCG 4 is set to R and theLCG 4 is allocated the PRACH resource (frequency resources of subframenumbers 3, 5, 7, and 8) with the exception of the PRACH resourceindicated by the PRACH mask index 1 (frequency resource of subframenumber 1) among the PRACH resource determined by the PRACH configurationindex 13 (frequency resource of subframe number 1, 3, 5, 7, and 8).

The eNB 610 sends the UE 605 the RRC Connection Reconfiguration messageincluding the DRB configuration information (drb-ToAddModList), logicalchannel configuration information (logicalChannelConfig), and PRACH maskindex list information at step 640. The PRACH mask index listinformation contains the PRACH mask index information of the logicalchannels/logical channel groups arranged in an order of the identifiersof the logical channels/logical channel groups configured to the UE 650.The PRACH mask index list information does not include the PRACH maskindex corresponding to the SRB/logical channel group 0, and the UE 605applies a value predetermined implicitly. If the PRACH mask index listinformation is not signaled, the UE 605 applies a value predeterminedimplicitly, e.g. PRACH mask index 0, to all of the logicalchannels/logical channel groups. For example, in the case that the UE605 is configured with the LCGs 0, 1, and 4, if the PRACH mask indexlist information includes 1 and 2, this means that the PRACH mask index1 is configured to the PRACH mask index 1, and the PRACH mask index 2 tothe LCG 2.

If the regular BSR is triggered at step 645, the procedure goes to step650 at which the UE determines whether any D-SR resource is allocated.If D-SR resource is allocated, this means that the UE is configured withthe PUCCH transmission resource for transmitting SR.

If the D-SR resource is allocated, the UE 605 triggers D-SR at step 655.That is, the UE transmits the SR using the PUCCH transmission resource.

If no D-SR resource is allocated, the procedure goes to step 660. Atstep 660, the UE 605 determines the PRACH resource for transmittingpreamble as follows.

1. If PRACH mask index list information is not signaled, the UEdetermines that all the PRACH resources indicated by the random accessresource configuration (prach-ConfigIndex) are the PRACH resourcesavailable for transmitting the preamble.

2. If PRACH mask index list information is signaled, then the UEoperates as follows.

-   -   The UE 605 checks the PRACH mask index of the LCH/LCG triggered        the regular BSR. The regular BSR is triggered when new data        occurs on the logical channel or the retxBSR-Timer expires. If        the BSR is triggered by the occurrence of new data, the UE        checks the PRACH mask index of the logical channel/logical        channel group of the data. If the regular BSR is triggered by        the expiry of the timer, the UE checks the PRACH mask index of        the logical channel/logical channel group of the data with the        highest priority among the data stored in the UE 605 and capable        of being transmitted at the corresponding time point.    -   The UE 605 checks the duplex mode of the current serving cell.        If the duplex mode is FDD, the UE 605 applies the PRACH resource        defined available for the FDD and, otherwise, if the duplex mode        is TDD, the PRACH resource defined available for TDD.    -   The UE 605 checks the random access resource configuration of        the serving cell to determine the PRACH resource configured to        the current serving cell.    -   The UE 605 determines the PRACH resource in the intersection        between the available PRACH resource indicated by the PRACH mask        index and the PRACH resource configured to the serving cell as        the PRACH resource available for transmitting the preamble.

The UE 605 transmits the preamble using the resource selected among thePRACH resources available for transmitting the preamble at step 665. Forexample, the UE 605 may select the PRACH resource configured for thetime point closest to the current time among the PRACH resources.

<Third Embodiment>

The PDCP sequence number is 7-bit or 12-bit wide. By taking notice thata PDCP SDU corresponds to an IP packet and a normal IP packet has themaximum size of 1500 bytes, the 12-bit sequence number restricts thepeak data rate to 0.88 Gbps under the assumption that the Round TripTime (RTT) of the PDCP end is 25 ms in handover. In consideration of thetendency of increase in transmission speed of the LTE-A mobilecommunication system, the peak data rate of 1 Gbps is not enough. Inthis embodiment, a long sequence number (hereinafter, referred to asextended sequence number) is introduce to increase the peak data rate.

The LTE/LTE-A mobile communication system has been evolved from theinitial version of Rel-8 stipulating new release every one or one and ahalf year. The extended sequence number is expected to be introduced inRel-11 or Rel-12 and thus the term ‘new release’ is used to refer to therelease in which the extended sequence number is introduced and the term‘legacy release’ to the release before the extended sequence number isintroduced. The eNB of new release (hereinafter, referred to as new eNB)is capable of configuring the extended sequence number to the UE whilethe eNB of the legacy release (hereinafter, referred to as legacy eNB)neither understands nor use the extended sequence number. The length ofthe extended sequence number may be considered diversely, it seems to beappropriate to extend the sequence number to 15 bits using the threereserved bits of the current format by taking notice of the current PDCPPDU format. Although the sequence number is extended to 15 bits in thisembodiment, the length of the extended sequence number may be determineddifferently. Also, the legacy sequence number field may have a certainlength instead of 7 or 12 bits. The present embodiment is applicable toany case in which the sequence number is changed.

FIG. 7A is a diagram illustrating a PDCP PDU format having a 7-bitsequence number.

FIG. 7B is a diagram illustrating a PDCP PDU formation having a 12-bitsequence number.

FIG. 7C is a diagram illustrating a PDCP PDU format having a 15-bitsequence number (extended sequence number).

The PDCP PDU having the extended sequence number includes a 1-bit D/Cfield 725, a 15-bit sequence number 730, and a data field. The PDCP PDUhaving the 12-bit sequence number includes a 1-bit D/C field 715, 12-bitsequence number 725, and a data field. The PDCP PDU having the 7-bitsequence number includes a 1-bit D/C field 705, a 7-bit sequence number710, and a data field. The D/C field indicates whether the correspondingPDU is a data (D) PDU or a control (C) PDU. The data field containsupper layer data such as IP packet. In the case that the UE performshandover from a legacy eNB to a new eNB or from a new eNB to a legacyeNB, the length of the PDCP sequence number may change. The eNB controlssuch that the UE adjusts the related-parameters in adaptation to thechange of the length of the sequence number in the course of the PDCPoperation or releases the current PDCP and configured the PDCP newly.The former case may be of handover from the legacy eNB to the new eNB,and the latter case may be of the handover from the new eNB to thelegacy eNB.

FIG. 8 is a signal flow diagram illustrating the handover procedureaccording to the third embodiment of the present invention. In FIG. 8,the mobile communication system includes a UE 805, a source eNB 810, anda target eNB 815. The source eNB 810 makes a handover decision to thetarget eNB 815. The handover decision is made in consideration of theload status of the current cell and channel condition of the UE 805. Thesource eNB 810 sends the target eNB 815 a control message requesting forhandover at step 825. This message may include informations as follows.

1. Target Cell ID: Identifier of the handover target cell

2. E-RABs To Be Setup List: E-RAB corresponds to radio bearer andEvolved Packet System (EPS) bearer and is identified by the eps beareridentifier (eps-bearerIdentity). This information includeseps-bearerIdentity per EPS bearer and required QoS information. Thebearer is a path of processing data requiring a predetermined QoS andreferred to as EPS bearer between the UE 805 and S-GW and E-RAB betweenthe UE 805 and eNB. One or two radio bearers are established per E-RAB.

3. RRC Context: Various configuration information configured to the UE805 by the source eNB 810 and capability information of the UE 805 (e.g.extended PDCP Sequence Number (SN) supportability).

The target eNB 815 sends the source eNB 810 a control message foraccepting the handover at step 830, the control message including theinformations as follows.

1. E-RABs Admitted List: List of E-RABs configured by the target eNB815. The target eNB 815 may configure some of the E-RABs requested bythe source eNB 810.

2. Target eNB To Source eNB Transparent Container: This contains thecontrol information transmitted from the target eNB 815 to the UE 805.In more detail, this includes the RRC message instructing handover. Ifthe release of the source eNB 810 is higher than that of the target eNB815 or if the source eNB 810 uses the extended PDCP SN but the targeteNB 815 does not, the handover command message includes the controlinformation instructing to release the Data Radio Bearer (DRB) with theextended PDCP SN and to establish a new DRB corresponding to the EPSbearer linked to the DRB. The newly established DRB is configured to donot use the extended PDCP SN. If the release of the target eNB 815 ishigher than that of the source eNB 810 or if the source eNB 810 uses thenormal PDCP SN but the target eNB 815 uses the extended PDCP SN, thecontrol information instructing the UE 805 to continue performing PDCPoperation may be included. The control information may be an indicatorof instructing the use of the extended PDCP NS.

The source eNB 810 sends the UE 805 an RRC control message instructinghandover at step 835. The control message includes the informations asfollows.

1. Mobility Control Information (mobilityControlInfo): Targetcell-related information, e.g. information including frequency and PCIof the target cell.

2. Radio Resource Configuration Information(radioResourceConfigDedicated): DRB configuration information to beapplied to the target cell. The Data Radio Bearer (DRB) is mapped to theEPS bearer one by one, and the mapping relationship between DRB and EPSbearer is indicated by the eps bearer identifier included in the DRBconfiguration information. In the case where a certain EPS bearer x ismapped to a certain DRB y for which the extended PDCP sequence number isused, if the UE 805 is handed over to an eNB which does not support theextended PDCP sequence number, the eNB commands the UE 805 to releasethe DRB y and establish a new DRB z for which the normal PDCP sequencenumber is used and which is mapped to the EPS bearer x. This operationis possible by including fullConfig in the RRCConnectionReconfigurationmessage (hereinafter, referred to as signaling scheme 1) or includingthe control information for releasing the DRB linked to the EPS bearerand the control information for link of a newly configured DRB to theEPS bearer in one RRC control message (hereinafter, referred to assignaling scheme 2). If the fullConfig is included in theRRCConnectionReconfiguration message, this means releasing all of theDRBs configured by the current RRC configuration, e.g. DRB configurationinformation, and setting up DRB by applying the new DRB configurationinformation included in the RRCConnectionReconfiguration message. Thiscan be understood as instructing to release the configuration based onthe previous configuration information automatically and is advantageousin terms of reducing overhead as compared to instructing release per DRBexplicitly. Hereinafter, releasing DRB and reconfiguring a new one basedon the fullConfig is referred to as first case. In the case of changingthe normal PDCP SN to the extended PDCP SN in the course of handover,the PDCP configuration information of the control information includesan indicator instructing the use of the extended PDCP SN. If the controlmessage instructing handover in the situation of using the normal PDCPSN and if the control message includes the indicator instructing to usethe extended PDCP SN, the UE 805 adjusts the PDCP SN and relatedparameters in the course of the PDCP operation. Adjusting the PDCP SNand related parameters, maintaining the DRB, is referred to as secondcase.

If the RRC Connection Reconfiguration message received at step 835includes the fullConfig (i.e. the first case), the UE performs steps840, 845, and 850. If the information included the RRC ConnectionReconfiguration message received at step 835 fulfils the followingcondition (i.e. the second case), the procedure goes to step 853.

<condition>

The normal PDCP SN is used before the receipt of the RRC ConnectionReconfiguration message, and the RRC Connection Reconfiguration messageindicates use of the extended PDCP SN

The UE 805 releases the DRB indicated in the message at step 840. If thesignaling scheme 2 has been used, the UE 805 releases the DRB indicatedby the drb-identity included in the control information calleddrb-ToReleaseList. At this time, the UE 805 releases the RLC first andthen the PDCP. If the signaling scheme 1 has been used, the UE releasesthe DRBs mapped to the EPS bearer identifiers (eps-BearerIdentity)listed in the drb-ToAddModList. In other expression, the UE releases theDRBs mapped to the eps bearer identifiers (eps-BearerIdentity) belongingto the current UE configuration among the eps bearer identifiers(eps-BearerIdentity) listed in the drb-ToAddModList. Releasing a DRBmeans discarding data stored at PDCP transmission/reception entities andRLC transmission/reception entities and releasing the entities.Otherwise if the condition is fulfilled, the UE 805 releases the DRBwithout discarding the data. Detailed description thereof is made inmore detail with reference to step 850.

At step 845, the UE 805 sets up the DRB indicated in the controlmessage. The UE 805 sets up the DRB by referencing the drb-ToAddModList.The drb-ToAddModList forms a code formatted as follows.

<code>----------------------------------------------------------------------DRB-ToAddModList ::= SEQUENCE (SIZE (1..maxDRB)) OF DRB-ToAddModDRB-ToAddMod ::= SEQUENCE { eps-BearerIdentity INTEGER (0..15) OPTIONAL,-- Cond DRB-Setup drb-Identity DRB-Identity, pdcp-Config PDCP-ConfigOPTIONAL, -- Cond PDCP rlc-Config RLC-Config OPTIONAL, -- Cond SetuplogicalChannelIdentity INTEGER (3..10) OPTIONAL, -- Cond DRB-SetuplogicalChannelConfig LogicalChannelConfig OPTIONAL, -- Cond Setup ... }----------------------------------------------------------------------

At step 850, the UE 805 checks the DRBs fulfilling the followingconditions. If the signaling scheme 1 has been used, the UE 805 deliversthe downlink data stored in the released DRB which fulfills thefollowing conditions to the upper layer other than discarding.

1. In the case that the signaling scheme 1 has been used, if the DRBwhose eps-BearerIdentity value is included in the DRB-TAddModList and ispart of the current UE configuration, i.e., in the case receiving theRRC Connection Reconfiguration message including fullConfig, if theesp-BearerIdentity mapped to any of currently configured DRB is includedin the drb-ToAddModList too, it is determined that the DRB indicated bythe esp-bearerIdentity fulfils the condition in the currentconfiguration.

2. In the case that the signaling scheme 2 has been used, if a DRBcorresponding to an certain eps-bearerIdentity is released and a new DRBcorresponding to the eps-bearerIdentity is set up through one RRCcontrol message (if a DRB associated with an eps-bearerIdentity isreleased and a new DRB is added and associated with theesp-bearerIdentity in the same message), it is determined that thecorresponding DRB fulfils the condition.

For the DRB fulfilling the above conditions, the UE does not discard thedata stored in the DRB right before being released but delivers thedownlink data to the upper layer and transmits the uplink data to thenewly established DRB. The downlink data stored in the DRB means thedata to be segmented into RLC SDU and the data stored in the PDCP windowamong the data stored in the RLC reception buffer. As described above,by releasing the RLC first and then the PDCP, the data stored in the RLCis delivered to the PDCP (from the viewpoint of the RLC, PDCP is theupper layer which has upper layer such as IP layer). The uplink datastored in the DRB means the data stored in the transmission buffer ofthe PDCP. In more detail, the data stored in the PDCP transmissionbuffer may include following data.

1. type 1 data: data which has never delivered the upper layer yet (PDCPSDU for which on PDU has been submitted to the lower layer yet).

2. type 2 data: SDU having the lowest sequence number among the datawhich has been delivered to the lower layer but its successfultransmission has not be determined and SDUs subsequent thereto (PDCPSDUs for which a corresponding PDU has been submitted to lower layersprior to the PDCP release, starting from the first SDU for which thedelivery of the corresponding PDUs has not been confirmed by the lowerlayer). Also, only the data which have been delivered to the lower layerand of which successful transmission is not determined yet may bedetermined as the type 2 data.

FIG. 9 is a diagram illustrating the local transfer according to thethird embodiment of the present invention.

FIG. example, when the PDCP is released, if the PDCP transmission bufferhas data up to PDCP SDU [100], data of up to PDCP SDU [80] have beentransmitted, and the transmission of data of PDCP SDUs [75] and [70] arenot confirmed, the PDCP SDUs [81] to are the type 1 data and the PDCPSDUs [75] to [85] are the type 2 data. Or, the type 2 data correspond tothe PDCP SDUs [75] and [70]. The UE performs local transfer on the type1 data 915 and the type 2 data 920 of the PDCP 905 which is released forthe DRB fulfilling the above condition to the PDCP 910 set up newly inmapping with the same eps bearer identifier (eps-bearerIdentity). Atthis time, the PDCP SDUs are transferred in the same order as the PDCPSDU COUNT. Or, the PDCP SDUs are transferred in the order as they arrive(i.e. first arrived first transferred). The COUNT is a sequence numberfor use in encryption/de-encryption at PDCP and has a length of 32 bitsincluding Hyper Frame Number (HFN) of [32-n] bits and PDCP SN of n bits.Here, n denotes the length of PDCP SN.

At step 853, the UE reestablishes the PDCP entity and the RLC entity. Ifthe RLC entity is established, it assembles all available RLC SDUs amongthe RLC PDUs stored in the reception buffer of the RLC entity into PDCPPDUs and transfers the PDCP PDUs to the PDCP entity. The PDCP entityprocesses the PDCP PDUs transferred by the RLC entity. In more detail,the UE 805 performs PDCP SN adjustment operation on the PDCP PDUs. ThePDCP SN adjustment operation is performed when the normal PDCP SN ischanged to the extended PDCP SN or vice versa. In the following, thedescription is directed to the case where the normal PDCP SN is changedto the extended PDCP SN. In the course of the PDCP SN adjustmentoperation, the reception-related parameter may be applied to the PDCPPDUs having the normal PDCP SN independently or after processing all thePDCP PDUs having eh normal PDCP SN.

[PDCP SN Adjustment Operation]

1. Identify DRBs indicated to switch from the normal PDCP SN to theextended PDCP SN (e.g. DRBs connected to RLC AM)

2. Adjust the parameters of the identified DRBs as follows.

-   -   Add 2 Most Significant Bits (MSBs) to the Next_PDCP_TX_SN. The 2        bits are 2 LSBs of TX_HFN.    -   Remove 2 LSBs of TX_HFN    -   ADD 2 MSBs to Next_PDCP_RX_SN. The 2 bits are 2 LSBs of RX_HFN.    -   Remove 2 LSBs of RX_HFN    -   Add 2 MSBs to Last_Submitted_PDCP_RX_SN. The 2 bits are 2 LSBs        of RX_HFN or a value obtained by subtracting 1 from 2 LSBs of        RX_HFN.        -   If the difference between the previous            Last_Submitted_PDCP_RX_SN and the previous Next_PDCP_RX_SN            is equal to or less than a predetermined value (i.e. half of            the total number of normal PDCP SNs, or 2048), the 2 LSBs of            RX_HFN are used. If the difference is greater than the            predetermined value, a value obtained by subtracting 1 from            the 2 LSBs of RX_HFN (e.g. 10 if the 2 LSBs are 11) is used.

The Next_PDCP_TX_SN denotes a variable storing the PDCP SN to be appliedto the next PDCP SDU. The TX_HFN denotes the HFN related to theNext_PDCP_TX_SN. The COUNT to be applied to the next PDCP SDU isobtained by concatenating the TX_HFN and Next_PDCP_TX_SN.

The Next_PDCP_RX_SN denotes the parameter storing the PDCP SN of thePDCP PDU expected to be received next. The RX_HFN denotes the HFNrelated to the Next_PDCP_RX_SN. The COUNT to be applied to the PDCP SDUexpected to be received next is acquired by concatenating the RX_HFN andNext_PDCP_RX_SN.

The Last_Submitted_PDCP_RX_SN denotes the PDCP SN of the last PDCP SDUdelivered to the upper layer.

The source eNB 810 forwards the following SDUs to the target eNB 815 atstep 855.

1. PDCP SDUs that have never been transmitted to the UE 805 yet

2. Data which has been transmitted to the UE 805 but of which successfultransmission has not been confirmed at the lower layer.

The UE 805 acquires downlink synchronization with the target cell andperforms random access procedure at step 860. If the random accesscompletes successfully, the UE determines that the handover hascompleted successfully and thus transmits the RRC ConnectionReconfiguration Complete message.

The UE 805 and the eNB operate as follows at step 865.

<operation>

In the first case, the UE 805 and the target eNB 815 initialize theHyper Frame Number (HFN) and PDCP SN to 0, and the target eNB 815 sendsthe UE 805 the PDCP SDUs received from the source eNB 810 sequentially.

In the second case, the target eNB 815 performs PDCP SN adjustmentprocedure and transmits a PDCP STATUS REPORT. The target eNB alsotransmits/receives PDCP SDUs that are requested for retransmission inthe PDCP STATUS REPORT transmitted by the UE 805. The UE 805 transmitsthe PDCP STATUS REPORT and transmits/receives the PDCP SDUs requestedfor retransmission in the PDCP STATUS REPORT transmitted by the eNB. ThePDCP STATUS REPORT includes the First Mission PDCP SN (FMS) informationcorresponding to the size of the extended PDCP SN.

FIG. 10 is a flowchart illustrating the handover procedure of the UE 805according to the third embodiment of the present invention.

The UE 805 receives PDCP configuration information for a predeterminedDRB at step 1005. The PDCP configuration information is transmitted tothe UE 805 in the information called drb-ToAddModList.

The UE determines whether the DRB is RLC UM bearer or RLC AM bearer atstep 1010. If the DRB is the AM bearer, the procedure goes to step 1015and, otherwise, step 1025. The RLC UM bearer is the bearer configuredfor use in RLC UM mode, and the RLC AM bearer is the bearer configuredfor use in RLC AM mode. The RLC UM (Unacknowledged Mode) is theoperation mode operating without Automatic Request (ARQ), and the RLC AM(Acknowledged Mode) is the operation mode operating with ARQ.

At step 1015, the UE 805 checks whether the PDCP configurationinformation includes the control information called extendedHeader asthe indicator indicating the use of the extended sequence number and, ifso, determines to use the 15-bit sequence number and, otherwise, the12-bit sequence number.

At step 1025, the UE 805 checks whether the PDCP configurationinformation includes the control information called PDCP-SN-size and, ifso, uses the sequence number length indicated in the controlinformation. The sequence number length is 7 bits or 12 bits.

As described above, the PDCP SN of the RLC AM bearer is indicated by theextendedHeader field, and the PDCP SN of the RLC UM bearer is indicatedby the pdcp-SN-size. By using different fields, it is possible to limitthe length of each field to 1 bit. In order to notify of one of the7-bit, 12-bit, and 15-bit length, it is necessary to use a 2-bit field.

The UE 805 determines whether it is the first case or the second case atstep 1030. If it is the first case, the procedure goes to step 1045 and,otherwise, step 1035.

At step 1035, the UE 8085 reestablishes PDCP and RLC sequentially. Atstep 1040, the UE 805 performs the PDCP SN adjustment procedure asfollows.

1. If the PDCP-config of step 1005 includes the extendedHeader and ifthe normal PDCP SN has been used before the receipt of the information,the UE performs the PDCP SN adjustment procedure.

2. If the PDCP-config of step 1005 includes no extendedHeader and if theextended PDCP SN has been used before the receipt of the information,the UE performs PDCP SN adjustment.

3. In other cases, the UE does not perform the PDCP SN adjustmentprocedure.

At step 1045, if the corresponding DRB is configured for generating thePDCP STATUS REPORT, the UE 805 generates the PDCP STATUS REPORT. Or ifthe corresponding DRB is configured to generate the PDCP STATUS REPORTand if the PDCP SN length is not changed, the UE generates the PDCPSTATUS REPORT. The UE 805 determines the size of the FMS field to beapplied to the PDCP STATUS REPORT as follows.

1. If the PDCP-config of step 1005 includes the extendedHeader, the UEconfigures the 15-bit FMS field of the PDCP STATUS REPORT.

2. If the PDCP-config of step 1005 includes not extendedHeader and theextended PDCP SN has been used already before the reception of theinformation, the UE configures the 12-bit FMS field of the PDCP STATUSREPORT.

3. If the PDCP-config of step 1005 includes no extendedHeader and if thenormal PDCP SN has been used before the receipt of the information, theUE configures 12-bit FMS field of the PDCP STATUS REPORT.

At step 1045, the UE determines whether the newly configured PDCP andthe eps-bearerIdentity of the DRB exist in the current configuration atstep 1045. That is, the UE determines whether there is any DRB identicalin eps-bearerIdentity with the newly configured DRB among the DRBsconfigured to the UE 805 before the receipt of the RRC control messageincluding the fullConfig. If so, the procedure goes to step 1060 and,otherwise, step 1050. At step 1050, the UE releases the RLC entity ofthe DRB. If two RLC entities are configured on the DRB, the UE releasesboth the two RLC entities. Also, the UE assembles the RLC SDUs than canbe assembled among the out-of-sequence data stored in the receptionbuffer of the RLC entity and delivers the assembled PDCP PDUs to theupper layer, i.e. PDCP layer.

At step 1055, the UE 805 releases the PDCP entity of the DRB. The UEdelivers all of the out-of-sequence PDCP SDUs stored in the receptionbuffer of the PDCP to the upper layer. The UE also transferspredetermined data among the data stored in the transmission buffer ofthe PDCP, i.e. type 1 data and type 2 data, to the PDCP transmissionbuffer of the newly configured PDCP entity.

Unlike the conventional method of releasing the PDCP entity first andthen the RLC entity, the method of this embodiment releases the RLCentity first and then the PDCP entity such that the out-of-sequence datastored in the reception buffer can be delivered to the upper layerbefore the release of the DRB.

The UE 805 resumes the communication by applying the new configurationat step 1060.

FIG. 11 is a diagram illustrating a format of the PDCP STATUS REPORTaccording to the third embodiment of the present invention.

The PDCP STATUS REPORT is a control message exchanged between the PDCPtransmitter and receiver to avoid packet loss in the case that the RLCcannot perform ARQ temporarily due to the reconfiguration of the RLCentity. The PDCP STATUS REPORT includes a D/C field 1105, a PDU typefield 1110, an FMS field 1115, and a bitmap field 1120. The D/C field1105 is 1-byte long and indicates whether the corresponding PDCP PDU isa data PDU or a control PDU. The PDCP STATUS REPORT is a control PDU.The PDU type field 1110 is 3-bit long and indicates the type of thecontrol PDU. The FMS field 1115 is 12-bit or 15-bit long. The FMSrecorded at the FMS field 1115 indicates the PDCP SN of the firstmissing PDCP packet. The bitmap 1120 is variable in length and each bitof the bitmap indicates presence/absence of PDCP packet to receive ornecessity of retransmission. The PDCP SN corresponding to each bit ofthe bitmap is determined depending on the FMS and the position of thecorresponding bit on the bitmap. For example, if the FMS is set to 1,the first and second bits indicate the PDCP SN 2 and PDCP SN 3respectively.

<Fourth Embodiment>

Only when any SCell is configured or activated to the UE or the SCell isreleased or deactivated, the UE may reconfigure the Radio FrequencyFrontend. This includes the procedure of reconfiguring the RF filterbandwidth in adaptation to the situation in which the SCell isconfigured or activated newly or released or deactivated, and the datacommunication is suspended while the UE is reconfiguring the bandwidth.The RF bandwidth reconfiguration is characterized as follows.

If an SCell is configured, activated, released, or deactivated on thesame frequency band as the serving cell configured ready (e.g. PCell),the data communication is suspended in the previously configured servingcell (e.g. the PCell) during a predetermined period. For explanationconvenience, it is assumed that the previously configured serving cellis the PCell and the suspension of the data communication is referred toas PCell interruption.

The determination on whether PCell interruption has occurred and thelength of the PCell interruption period are determined depending on theUE processing capability and hardware performance.

1. If the PCell and SCell are configured on different frequency bands;the RF bandwidth reconfiguration is not necessary, and the PCellinterruption does not occur.

2. If the PCell and SCell are configured on the same frequency band, ifthe UE has at least one RF device (or reception device), and if at leastone RF device (or reception device) operates on the frequency band; theRF bandwidth reconfiguration is not necessary, and the PCellinterruption does not occurs.

3. If the PCell and SCell are configured on the same frequency band onwhich only one RF device operates, the RF bandwidth reconfiguration isnot necessary, and the PCell interruption occurs.

In the case of performing RF bandwidth reconfiguration due to the SCellactivation or deactivation, the PCell interruption occurs before andafter performing measurement on the SCell in the inactive state. If theRF device is reconfigured to include all the PCell and SCell inconfiguring the SCell and configured to include only the PCell inreleasing the SCell, the PCell interruption does not occur while theSCell is in configured state.

The present embodiment proposes a scheduling method and apparatusoperating in such a way that the UE reports to the eNB whether the PCellinterruption is necessary and then the eNB schedules the UE inconsideration of whether the PCell interruption has occurred and, if so,the occurrence time.

FIG. 12 is a signal flow diagram illustrating a communication procedureaccording to the fourth embodiment of the present invention. In FIG. 12,the system includes a UE 1205, an eNB 1210, and an MME 1215. The UE 1205powers on at step 1220. The UE 1205 searches for the cell of which theelectric wave is received and the corresponding PLMN and determines thecell and PLMN to perform the registration procedure based thereon atstep 1225.

The UE 1205 sends the MME a control message requesting for registration(ATTACH REQUEST) through the selected cell after the RRC connectionsetup procedure at step 1230. This message includes the information suchas identifier of the UE 1205. Upon receipt of the ATTACH REQUESTmessage, the MME 1215 determines whether to accept the registration and,if it is determined to accept, sends the serving eNB 1210 a controlmessage (Initial Context Setup Request) at step 1235. If the MME has theUE capability information, it transmits the UE capability information inthe control message; however, the MME has no UE capability informationin the initial registration procedure and thus the control messageincludes not UE capability information. If the Initial Context SetupRequest message having no UE capability information, the eNB 1210 sendsthe UE 1205 a control message called UE CAPABILITY ENQUORY to acquirethe UE capability information at step 1240. This message is ofinstructing the UE 1205 to report the UE capability such as Radio AccessTechnology (RAT) of the UE 1205 using the parameter called RAT type. Ifthe UE 1205 is performing the procedure in the LTE network, the RAT typeis set to Evolved Universal Terrestrial Radio Access (EUTRA). The eNBmay request for the UMTS-related capability information of the UE 1205by adding another RAT type of UTRA for preparing handover afterward ifthere is other radio network, e.g. UMTS network, around. If the UECAPABILITY ENQUIRY control message is received, the UE generates UECAPABILITY INFORMATION including its capability information about theradio technology indicated by the RAT type. This control messagecontains the information on one or more bands combination informationson the bands combinations it supports. The band combination informationindicates the CA combinations supported by the UE 1205, and the eNB 1210configures appropriate CA to the UE 1205 based on this information. Theabove control message also includes the information indicating whetherthe PCell interruption is necessary for predetermined band combinationsof the UE 1205 (PCell interruption information). The UE 1205 sends theeNB 1210 the UE CAPABILITY INFORMATION message at step 1245. The eNB1210 sends the MME 1215 a UE CAPABILITY INFO INDICATION message toreport the UE capability information included in the UE CAPABILITYINFORMATION message to the MME 1215 at step 1250. The eNB 1210reconfigures the UE 1205 appropriately in consideration of the trafficstatus and channel condition of the UE 1205 based on the capabilityinformation reported by the UE 1205. For example, the eNB configuresadditional SCell or measurement gap with the command of instructingmeasurement on other frequencies at step 1255.

The eNB performs scheduling in the PCell in consideration of the PCellinterruption, and the UE 1205 performs RF bandwidth reconfiguration forPCell interruption during a predetermined period at step 1260.

FIG. 13 is a flowchart illustrating the SCell configuration messageprocessing procedure according to the fourth embodiment of the presentinvention.

The UE 1205 reports its capability to the eNB 1210 at step 1305. At thistime, the UE 1205 reports the frequency bands it supports and thefrequency bands combinations supporting carrier aggregation. The UEcapability report message includes 1-bit information indicating whetherthe PCell interruption is required.

The UE 1205 receives a control message requesting for configuring atleast one SCell at step 1310. The UE 1205 determines whether thefrequency of the SCell belongs to the same frequency band as the servingcell configured already, e.g. PCell, and is a neighboring frequency atstep 1315. If the above condition is not fulfilled, the UE 1205 does notperform the RF bandwidth reconfiguration at step 1320.

If the new SCell is configured on the same frequency band as the PCelland the frequencies of the two serving cells are adjacent to each other,the UE 1205 determines whether at least one of the following conditionsis fulfilled at step 1325.

Condition 1: The capability report indicates that PCell interruption isnot necessary.

Condition 2: The scellMeasurementCycle or the greatest one betweencurrent DRX cycle and the scellMeasurementCycle is less than apredetermined threshold value.

If at least one of the two conditions is fulfilled, the UE 1205 skips RFbandwidth reconfiguration at step 1320.

If both the conditions are not fulfilled, the UE 1205 performs RFbandwidth reconfiguration during a predetermined period at step 1330.The predetermined period is the time period between the subframe (n+x1)and the subframe (n+x1+d). The x1 denotes the time necessary forreceiving and interpreting the RRC Connection Reconfiguration messageand taking an appropriate action and is set to a value large enough tobe applied to the UEs having various capabilities. Here, d denotes thetime required for reconfiguring RF bandwidth and may be set to a valuelarge enough to be applied to the UEs having various capabilities.

FIG. 14 is a flowchart illustrating the A/C MAC CE message processingprocedure of the UE 1205 according to an embodiment of the presentinvention.

Since steps 1405 is identical with step 1305, detailed descriptionthereof is omitted herein. The UE 1205 receives anActivation/Deactivation MAC CE (A/D MAC CE) in which a bit correspondingto at least one SCell is set to 1. The A/D MAC CE is a MAC layer controlmessage for activating or deactivating the SCells configured to the UE1205 and includes a MAC sub-header and payload. The MAC sub-headerincludes a Logical Channel ID (LCID) indicating the type of the payloadand an E bit indicating whether another MAC sub-header exists.

FIG. 14 is a flowchart illustrating the A/C MAC CE message processingprocedure of the UE 1205 according to an embodiment of the presentinvention.

The payload is a bitmap of 1 byte of which the C₇ bit 1505 indicates thestate of the serving cell of which SCell index is 7 (hereinafter, theserving cell of which SCell index is x is referred to as SCell x), theC₄ bit 1510 the state of the SCell 4, and the C₁ bit 1515 the state ofthe SCell 1. In the case that the bit corresponding to the SCell x isset to 1, if the SCell x is in the active state already, the UE 1205maintains the active state and, otherwise if the SCell x is in theinactive state, transitions the SCell state to the active state. In thecase that the bit corresponding to the SCell x is set to 0, if thecorresponding SCell is in the active state, the UE transitions the SCellstate to the inactive state and, otherwise if the corresponding SCell isin the inactive state, maintains the inactive state.

The UE 1205 determines whether the SCell of which corresponding bit isset to 1 is the SCell which has been activated already at step 1415. Ifthe SCell has been already activated, the procedure goes to step 1425and, otherwise, step 1420. At step 1420, the UE 1205 determines whetherthe frequency of the SCell belongs to the same frequency band as theserving cell configured already, e.g. PCell, and adjacent to thefrequency of the PCell. If the condition is not fulfilled, the proceduregoes to step 1425 and, otherwise the condition is fulfilled, step 1430.At step 1425, the UE 1205 starts performing operation 1 at subframe(n+x3) without RF bandwidth reconfiguration. The operation 1 includesthe normal actions taken in activating the SCell as follows.

Operation 1

Transmit Sounding Reference Signal (SRS) in active SCell

Transmit Channel Quality Indicator (CQI) for SCell

Monitor PDCCH of SCell

Monitor PDCCH for SCell (SCell scheduling may be performed by the PCelldepending on the configuration, and PDCCH monitoring for SCell meansthat the UE 1205 monitors PDCCH of the PCell to determine whether SCellscheduling is received)

Start sCellDeactivationTimer

Trigger Power Headroom Report (PHR)

If the RF bandwidth reconfiguration is not performed, x3 is set to aperiod long enough to complete the above operation at the UE 1205, e.g.period corresponding to 8 subframes.

The UE 1205 determines whether at least one of following conditions isfulfilled at step 1430.

Condition 1: The capability report indicates that the PCell interruptionis not necessary.

Condition 2: scellMeasurementCycle or the greatest value between thecurrent DRX cycle and scellMeasurementCycle is less than a predeterminedthreshold value.

If at least one of the two conditions is fulfilled, the procedure goesto step 1425. Otherwise if both the conditions are not fulfilled, theprocedure goes to step 1435.

At step 1435, the UE 1205 perform RF bandwidth reconfiguration betweenn+x2 and n+x2+d. The x2 is set to a value, e.g. 5, in order for the UE1205 to transmit Hybrid Automatic Repeat Request (HARD) ACK incorrespondence to the A/D MAC CE. The UE 1205 performs operation 2 atthe first subframe after n+x2+d. The operation 2 has to be performeddirectly in the SCell after completion of the RF reconfiguration.

Operation 2

Transmit Sounding Reference Signal (SRS) in the SCell in active state

Monitor PDCCH of SCell

Monitor PDCCH for SCell (SCell scheduling may be performed by the PCelldepending on the configuration, and PDCCH monitoring for SCell meansthat the UE 1205 monitors PDCCH of the PCell to determine whether SCellscheduling is received)

The UE 1205 performs operation 3 at n+x3. The operation 3 is notperformed in the SCell directly and includes the actions taken atpredetermined timings although the RF reconfiguration has not beencompleted.

Operation 3

Start sCellDeactivationTimer

Trigger Power Headroom Report (PHR)

Transmit Channel Quality Indicator (CQI) for SCell

The sCellDeactivationTimer is of deactivating the SCell having no datato be transmitter/received during a predetermined period and configuredper SCell. If the SCell is activated, the UE 1205 starts the timer andrestarts the timer whenever downlink assignment or uplink grant for theSCell is received or whenever the SCell is reactivated.

The Power Headroom Report (PHR) is the control information of reportingthe current power headroom of the UE 1205 to the eNB 1210. If the SCellis activated, the UE 1205 reports power headroom (PHR) to the eNB 1210to notify the transmission power status for the SCell.

FIG. 16 is a block diagram illustrating a configuration of the UEaccording to an embodiment of the present invention.

Referring to FIG. 16, the UE according to an embodiment of the presentinvention includes a transceiver 1605, a controller 1610, amultiplexer/demultiplexer 1620, a control message processor 1635, andvarious higher layer processors 1625 and 1630.

The transceiver 1605 receives data and predetermined control signals onthe downlink channel of the serving cell and transmits data andpredetermined control signals on the uplink channel. In the case that aplurality of serving cells is configured, the transceiver 1605transmits/receives data and control signals through the plural servingcells.

The multiplexer/demultiplexer 1620 multiplexes the data generated by thehigher layer processors 1625 and 1630 and the control message processor1635 and demultiplexes the data received by the transceiver 1605, thedemultiplexed data being delivered to the higher layer processors 1625and 1630 or the control message processor 1635.

The control message processor 1635 is an RRC layer entity which takes anaction necessary for processing the control message received from theeNB. For example, the control message processor 1635 processes thereceived random access-related information and delivers the processingresult to the controller.

The higher layer processors 1625 and 1630 are established per service.The higher layer processor processes the data generated by the userservice such as File Transfer Protocol (FTP) and Voice over InternetProtocol (VoIP), the processing result being delivered to themultiplexer/demultiplexer 1620, and processes the data from themultiplexer/demultiplexer 1615, the processing result being delivered tothe higher layer service application.

The controller 1610 controls the transceiver 1605 and themultiplexer/demultiplexer 1615 to check the scheduling command, e.g.uplink grants, received by the transceiver 1605 and perform uplinktransmission using appropriate transmission resource at appropriatetiming. The controller controls overall operations related to the SCellconfiguration, PDCP sequence number processing, and random accesscongestion control. The controller 1610 may control the components ofthe UE to perform at least some of the above described embodiments.

FIG. 17 is a block diagram illustrating a configuration of the eNBaccording to an embodiment of the present invention.

Referring to FIG. 17, the eNB includes a transceiver 1705, a controller1710, a multiplexer/demultiplexer 1720, a control message processor1735, various higher layer processors 1725 and 1730, and a scheduler1715.

The transceiver transmits data and predetermined control signals on thedownlink channel of the serving cell and receives data and predeterminedcontrol signals on the uplink channel. In the case that a plurality ofcarriers is configured, the transceiver 1705 transmits/receives data andcontrol signals through the plural carriers.

The multiplexer/demultiplexer 1720 is responsible for multiplexing datagenerated by the higher layer processors 1725 and 1730 and the controlmessage processor 1735 or demultiplexing the data received by thetransceiver 1705, the demultiplexed data being delivered to the controlmessage processor 1735 or the controller 1710. The control messageprocessor 1735 processes the control message transmitted by the UE andtakes a necessary action or generates a control message to betransmitted to the UE, the generated control message being delivered tothe lower layer.

The higher layer processors 1725 and 1730 are established per serviceand processes the data from the S-GW or other eNB into RLC PDU, the RLCPDU being delivered to the multiplexer/demultiplexer 1720, and processesthe RLC PDU from the multiplexer/demultiplexer 1720 into PDCP SDU, thePDCP SDU being transmitted to the S-GW or other eNB.

The scheduler allocates transmission resource to the UE at anappropriate timing in consideration of the UE buffer status and channelstatus and controls the transceiver to process the signal to betransmitted to the UE and transmit the signal.

The controller 1710 controls overall operations related to the SCellconfiguration, PDCP sequence number processing, and random accesscongestion control.

The controller 1710 may control the components of the eNB to perform atleast some of the above described embodiments.

It will be understood that each block of the flowchart illustrationsand/or block diagrams, and combinations of blocks in the flowchartillustrations and/or block diagrams, can be implemented by computerprogram instructions. These computer program instructions may beprovided to a processor of a general purpose computer, special purposecomputer, or other programmable data processing apparatus to produce amachine, such that the instructions, which execute via the processor ofthe computer or other programmable data processing apparatus, createmeans for implementing the functions/acts specified in the flowchartand/or block diagram block or blocks. These computer programinstructions may also be stored in a computer-readable memory that candirect a computer or other programmable data processing apparatus tofunction in a particular manner, such that the instructions stored inthe computer-readable memory produce an article of manufacture includinginstruction means which implement the function/act specified in theflowchart and/or block diagram block or blocks. The computer programinstructions may also be loaded onto a computer or other programmabledata processing apparatus to cause a series of operational steps to beperformed on the computer or other programmable apparatus to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide steps forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Furthermore, the respective block diagrams may illustrate parts ofmodules, segments or codes including at least one or more executableinstructions for performing specific logic function(s). Moreover, itshould be noted that the functions of the blocks may be performed indifferent order in several modifications. For example, two successiveblocks may be performed substantially at the same time, or may beperformed in reverse order according to their functions.

The term “module” according to the embodiments of the invention, means,but is not limited to, a software or hardware component, such as a FieldProgrammable Gate Array (FPGA) or Application Specific IntegratedCircuit (ASIC), which performs certain tasks. A module mayadvantageously be configured to reside on the addressable storage mediumand configured to be executed on one or more processors. Thus, a modulemay include, by way of example, components, such as software components,object-oriented software components, class components and taskcomponents, processes, functions, attributes, procedures, subroutines,segments of program code, drivers, firmware, microcode, circuitry, data,databases, data structures, tables, arrays, and variables. Thefunctionality provided for in the components and modules may be combinedinto fewer components and modules or further separated into additionalcomponents and modules. In addition, the components and modules may beimplemented such that they execute one or more CPUs in a device or asecure multimedia card.

It is to be appreciated that those skilled in the art can change ormodify the embodiments without departing the technical concept of thisinvention. Accordingly, it should be understood that above-describedembodiments are essentially for illustrative purpose only but not in anyway for restriction thereto. Thus the scope of the invention should bedetermined by the appended claims and their legal equivalents ratherthan the specification, and various alterations and modifications withinthe definition and scope of the claims are included in the claims.

Although various embodiments of the present disclosure have beendescribed using specific terms, the specification and drawings are to beregarded in an illustrative rather than a restrictive sense in order tohelp understand the present invention. It is obvious to those skilled inthe art that various modifications and changes can be made theretowithout departing from the broader spirit and scope of the invention.

What is claimed is:
 1. A method performed by a terminal in acommunication system, the method comprising: communicating with a firstbase station based on a first radio bearer associated with a firstpacket data convergence protocol (PDCP) sequence number (SN) size;receiving, from the first base station, a message for a handover fromthe first base station to a second base station, wherein the messageincludes an indication of a full configuration and information on asecond radio bearer associated with a second PDCP SN size, the secondPDCP SN size being different from the first PDCP SN size; releasing allof configured data radio bearers (DRBs) including the first radiobearer, in response to the message including the indication of the fullconfiguration; establishing the second radio bearer associated with thesecond PDCP SN size based on the information included in the message;and communicating with the second base station based on the second radiobearer associated with the second PDCP SN size.
 2. The method of claim1, wherein a first PDCP entity for the first radio bearer is releasedbased on the indication of the full configuration, and wherein a secondPDCP entity for the second radio bearer is established based on theinformation included in the message.
 3. The method of claim 2, furthercomprising: delivering a downlink PDCP packet stored in the first PDCPentity to an upper layer before the first PDCP entity is released, incase that the first PDCP entity corresponds to a receiving PDCP entity.4. The method of claim 2, further comprising: discarding an uplink PDCPpacket stored in the first PDCP entity in case that the first PDCPentity corresponds to a transmitting PDCP entity.
 5. A method performedby a first base station in a communication system, the methodcomprising: communicating with a terminal based on a first radio bearerassociated with a first a packet data convergence protocol (PDCP)sequence number (SN) size; and transmitting, to the terminal, a messagefor a handover from the first base station to a second base station,wherein the message includes an indication of a full configuration andinformation on a second radio bearer associated with a second PDCP SNsize, the second PDCP SN size being different from the first PDCP SNsize, wherein all of configured data radio bearers (DRBs) including thefirst radio bearer is released by the terminal, in response to themessage including the indication of the full configuration, and whereinthe second radio bearer associated with the second PDCP SN size isestablished by the terminal based on the information included in themessage.
 6. The method of claim 5, wherein a first PDCP entity for thefirst radio bearer is released by the terminal based on the indicationof the full configuration, and wherein a second PDCP entity for thesecond radio bearer is established by the terminal based on theinformation included in the message.
 7. A method performed by a secondbase station in a communication system, the method comprising:communicating with a terminal based on a second radio bearer associatedwith a second packet data convergence protocol (PDCP) sequence number(SN) size, the second radio bearer being established by the terminalbased on information on the second radio bearer included in a messagefor a handover from a first base station to the second base stationtransmitted from the first base station to the terminal, wherein themessage includes an indication of a full configuration, wherein all ofconfigured data radio bearers (DRBs) including a first radio bearerassociated with a first PDCP SN size is released by the terminal, inresponse to the message including the indication of the fullconfiguration, and wherein the second PDCP SN size is different from thefirst PDCP SN size.
 8. The method of claim 7, wherein a first PDCPentity for the first radio bearer is released by the terminal based onthe indication of the full configuration, and wherein a second PDCPentity for the second radio bearer is established by the terminal basedon the information included in the message.
 9. A terminal in acommunication system, the terminal comprising: a transceiver; and acontroller configured to: communicate with a first base station based ona first radio bearer associated with a first packet data convergenceprotocol (PDCP) sequence number (SN) size, receive, from the first basestation, a message for a handover from the first base station to asecond base station, wherein the message includes an indication of afull configuration and information on a second radio bearer associatedwith a second PDCP SN size, the second PDCP SN size being different fromthe first PDCP SN size, release all of configured data radio bearers(DRBs) including the first radio bearer, in response to the messageincluding the indication of the full configuration, establish the secondradio bearer associated with the second PDCP SN size based on theinformation included in the message, and communicate with the secondbase station based on the second radio bearer associated with the secondPDCP SN size.
 10. The terminal of claim 9, wherein a first PDCP entityfor the first radio bearer is released based on the indication of thefull configuration, and wherein a second PDCP entity for the secondradio bearer is established based on the information included in themessage.
 11. The terminal of claim 10, wherein the controller is furtherconfigured to deliver a downlink PDCP packet stored in the first PDCPentity to an upper layer before the first PDCP entity is released, incase that the first PDCP entity corresponds to a receiving PDCP entity.12. The terminal of claim 10, wherein the controller is furtherconfigured to discard an uplink PDCP packet stored in the first PDCPentity in case that the first PDCP entity corresponds to a transmittingPDCP entity.
 13. A first base station in a communication system, thefirst base station comprising: a transceiver; and a controllerconfigured to: communicate with a terminal based on a first radio bearerassociated with a first a packet data convergence protocol (PDCP)sequence number (SN) size, and transmit, to the terminal, a message fora handover from the first base station to a second base station, whereinthe message includes an indication of a full configuration andinformation on a second radio bearer associated with a second PDCP SNsize, the second PDCP SN size being different from the first PDCP SNsize, wherein all of configured data radio bearers (DRBs) including thefirst radio bearer is released by the terminal, in response to themessage including the indication of the full configuration, and whereinthe second radio bearer associated with the second PDCP SN size isestablished by the terminal based on the information included in themessage.
 14. The first base station of claim 13, wherein a first PDCPentity for the first radio bearer is released by the terminal based onthe indication of the full configuration, and wherein a second PDCPentity for the second radio bearer is established by the terminal basedon the information included in the message.
 15. A second base station ina communication system, the second base station comprising: atransceiver; and a controller further configured to communicate with aterminal based on a second radio bearer associated with a second packetdata convergence protocol (PDCP) sequence number (SN) size, the secondradio bearer being established by the terminal based on information onthe second radio bearer included in a message for a handover from afirst base station to the second base station transmitted from the firstbase station to the terminal, wherein the message includes an indicationof a full configuration, wherein all of configured data radio bearers(DRBs) including a first radio bearer associated with a first PDCP SNsize is released by the terminal, in response to the message includingthe indication of the full configuration, and wherein the second PDCP SNsize is different from the first PDCP SN size.
 16. The second basestation of claim 15, wherein a first PDCP entity for the first radiobearer is released by the terminal based on the indication of the fullconfiguration, and wherein a second PDCP entity for the second radiobearer is established by the terminal based on the information includedin the message.